Many home and hospital diagnostic tests, such as glucose monitoring, utilize test strips with a reagent that under goes a colorimetric change upon contact with the glucose containing blood sample. However, commercially available reagent test strips have several limitations.
The patient using a prior art test strip must completely cover the reagent on the strip with a droplet of blood. Since there is no way for the blood to remain on the reagent by adhesion, most of the blood droplet adheres to the finger or other body appendage from which it was obtained by a lancet cut. Incomplete or uneven coverage of the reagent by the blood droplet results in uneven reaction with the reagent. Before the strips can be read, either visually or by a machine, the droplet of blood must be blotted off of the reagent. This often results in residual blood on the reagent if blotting is too gentle or a loss of reagent surface if the blotting is too rigorous. Each of the aforementioned limitations results in nonquantitative determinations. If borderline levels of the reactant are contained in the blood sample, even qualitative determinations can be inaccurate.
The semi-quantitative capability of prior art test strips has been recognized in the prior art. The U.S. Pat. No. 4,604,264 to Rothe et al, issued Aug. 5, 1986 discloses a test strip including a dry reagent containing film layer coating embedded at least preponderantly onto and into only one side of a carrier layer made of a multifilar fabric or fleece. The U.S. Pat. No. 3,715,192 to Wenz et al, issued Feb. 6, 1973 discloses an indicator strip, useful in analytical chemical procedures, which includes a reagent impregnated capillary material having at least a partially transparent film on one side and on the other side a film forming a hollow space which is in communication with the capillary material. The hollow space above the capillary material provides quicker absorption of a liquid material drawn onto a capillary material impregnated with the reagent. The patent states that it is necessary to submerge the end of the test strip including the capillary material and cover thereover into a liquid sample for the capillary material to be immersed in the sample. The main advantage of the construction is to enable the capillary material to absorb the liquid medium to be examined quickly to prevent chromotographic separation of the reagent during the absorption of the liquid media.
U.S. Pat. No. 4,088,484 to Lilja et al, issued May 9, 1978, discloses an apparatus for sampling with a cavity between two planar surfaces. A reagent is contained in the cavity and is dissolved with a sample drawn into the cavity by gravity, vacuum or capillary action. Analysis occurs by transmission of light across the optical path directly through the two planar surfaces. Hence, the amount of spacing between the surfaces must be critically controlled.
A related article entitled "Evaluation of `Hemo Cue`, a New Device for Determining Hemoglobin", CLINICAL CHEMISTRY, volume 32, Nov. 3, 1986, discloses a technique based on an optical measuring cuvet of a small volume and short light path. Reagents for lysing red blood cells are deposited on the inner walls of a cuvet cavity and a blood sample is drawn into the cavity by capillary action and mixed with the reagent. An instrument calculates the concentration of hemoglobin in the sample by the amount and color of light transmitted through the optical path containing the sample and displays the results. The "Hemo Cue".RTM. (registered trademark is owned by Leo Diagnostics AB Helsingborg, Sweden) comprises a pair of plastic plates having a space therebetween and a pointed edge. An area within the plates has the dry reagent deposited thereon. The reagent is mixed with the sample drawn into the space between the plates. Although "Hemo Cue".RTM. is shown to produce quantitative analysis, a sample is drawn through the communicating passageway and into the reagent containing area which is necessarily larger in volume than that needed for the quantitative measurement.
New lancing devices, such as disclosed in the U.S. patent application Ser. No. 764,051 to Dombrowski, filed Aug. 9, 1985, now U.S. Pat. No. 4,653,513, are capable of making incisions in body parts which are not highly vascularized. The device draws a small sample of blood from the incision. In combination with these devices, it is necessary that a test strip require a small amount of blood to make a quantitative determination, such as a glucose determination.
The present invention addresses the aforementioned limitations of the prior art by completely recovering and obtaining a very small precise volume of blood to evenly and completely cover a reagent surface. The device only draws an amount of blood quantitatively necessary to completely cover the reagent and produce a quantitative colorimetric reaction. The results of the reaction are not determined by light transmitted through a sample-reagent mixture, so the defined optical path length is not required.